Conventionally, impulse type display devices such as a CRT (Cathode Ray Tube), for example, and hold type display devices such as an LCD (Liquid Crystal Display), for example, are known as display devices. In the impulse type display device, focusing on an individual pixel, an on-period when an image is displayed and an off-period when an image is not displayed are repeated alternately. Even in a case where a motion picture is displayed, for example, human vision does not have an afterimage of a moving object, since an off-period is inserted when an image of one screen is rewritten. Therefore, a background and an object are clearly distinguished and a motion picture is viewed without any sense of discomfort. On the other hand, in the hold type display device, a luminance of an individual pixel is held during a whole frame period that is a rewrite period of an image of one screen. When a motion picture is displayed on this hold type display device, human vision has an afterimage of a moving object. Specifically, a moving object is viewed with an outline out of focus. Such a phenomenon is called such as a “motion blur” and considered to be caused by followability of human line of sight. Since the hold type display devices have such a motion blur for displaying a motion picture, conventionally, the impulse type display devices are generally employed for displays such as a TV which displays mainly motion pictures. Recently, however, displays such as a TV have been strongly required to be lighter or thinner, and hold type display devices which are easily made lighter or thinner have been increasingly employed rapidly for such displays.
Conventionally, the hold type display devices have also another problem that deterioration of image quality is caused by a low response speed of display elements. An overshoot drive is known for a drive method to suppress this image quality deterioration (e. g., Japanese Patent Application Laid Open No. 2004-233949). The overshoot drive is a drive method to provide a liquid crystal display panel, according to a combination of an input image signal of a previous frame and an input image signal of a current frame, with a higher drive voltage than a predetermined gradation voltage for the input image signal of the current frame or with a lower drive voltage than a predetermined gradation voltage for the input image signal of the current frame.
On the other hand, there is proposed an display device that performs image display by a pseudo impulse drive (hereinafter referred to as “pseudo-impulse drive”) where a frame period is divided into a period when an image is displayed (hereinafter referred to as “display period”) and a period when an image is not displayed (hereinafter referred to as “non-display period”), for suppressing the above mentioned motion blur (e.g., Japanese Patent Application Laid Open No. 2002-23707 and Japanese Patent Application Laid Open No. 2003-22061). FIG. 14 is a signal waveform diagram for explaining such a display device drive method. Here, a display device is assumed to have a plurality of (m) scanning signal lines GL1 to GLm (hereinafter also referred to as “the first row to m-th row scanning signal lines”). As shown in FIG. 14, when a pulse of a gate clock signal GCK is generated first after pulse generation of a gate start pulse signal GSP, a scanning signal supplied to the first row scanning signal line GL1 comes to exhibit a high level. A pulse width of the gate clock signal GCK corresponds to approximately a half of a conventional one horizontal scanning period, and, during a whole period corresponding to the pulse width, the scanning signal supplied to the first row scanning signal line GL1 is held at the high level. After that, according to pulse generation of the gate clock signal GCK, scanning signals supplied to scanning signal lines GL2, GL3, etc. below the first row, come to exhibit high levels sequentially and are held at the high levels during a whole period corresponding to approximately a half of the conventional one horizontal scanning period, respectively. After scanning signals supplied to all the scanning signal lines come to exhibit high levels in this manner each during a period corresponding to approximately a half of the conventional one horizontal scanning period, a pulse of the gate start pulse signal GSP is generated again. After that, according to pulse generation of the gate clock signal GCK, the scanning signals supplied to all the scanning signal lines again come to exhibit high levels sequentially and the high levels are held during a whole period corresponding to approximately a half of the conventional one horizontal scanning period. In this manner, one frame period (1f) is divided into two periods having the same length with each other (1f/2). For details, as shown in FIG. 15, one frame period is divided into two periods called sub-frames, and an image is displayed only in one sub-frame period (display period) and an image is not displayed in the other sub-frame period (non-display period). Thereby, a black image is inserted between a preceding image and a following image when an image of one screen is rewritten. As a result, human vision does not have an afterimage of a moving object and the motion blur is suppressed.    [Patent Document 1] Japanese Patent Application Laid Open No. 2004-233949    [Patent Document 2] Japanese Patent Application Laid Open No. 2002-23707    [Patent Document 3] Japanese Patent Application Laid Open No. 2003-22061